In-shoe center of pressure: Indirect force plate vs. direct insole measurement

Background: In-shoe center of pressure (COP) measurement is essential in biomechanics. COP can be measured directly utilizing pressure-sensitive insoles, or calculated indirectly via force plate-generated data. While the latter does not require the use of additional measurement hardware (shoe insoles), its precision at calculating in-shoe COP has not been determined. Our purpose was to ascertain the precision of force plate in-shoe COP calculations and enhance their accuracy through a mathematical algorithm. Methods: Twelve male students participated in the study. In-shoe COP was measured synchronously via the Pedar-X insole system and AMTI force plates, comparing the measurements of both systems. A mathematical algorithm was created to improve agreement between the systems and comparisons were recalculated. Results: The two methods showed different measurements of in-shoe COP. The medio-lateral (ML) and anterior-posterior (AP) Pearson correlation coefficients between systems were 0.44 ± 0.35 and 0.99 ± 0.01, and the ML and AP RMS errors were 6.3 ± 3.0. mm and 43.0 ± 12.5. mm, respectively. Using a mathematical algorithm, the differences between the measurements of each system could be reduced significantly (all P< 0.001). Conclusions: Without adjustment, force plates give an approximate location of the COP. Using an adjustment model greatly improves the accuracy of the COP trajectory during stance.